In the field of semiconductor radiation imaging devices comprising a semiconductor detector substrate solder bump-bonded to a semiconductor processing/readout substrate, the occurrence of “cold” solder joints can be a problem. See U.S. Pat. Nos. 5,379,336; 5,812,191; EP 1162833; and EP 0421869. Cold solder joints, also called cold welds, can occur in a variety of solder compositions, including solder alloys containing Indium, Lead, Tin and other metals.
This has motivated the field to seek alternative soldering or bump-bonding methods to reduce the occurrence of cold joints, including a low-temperature bump-bonding techniques (see U.S. Pat. No. 5,952,646). However, current soldering or the above mentioned bump-bonding techniques cannot fulfill all the requirements of new high-density, imaging device assembly processes which utilize temperature sensitive semiconductor materials in the detector substrates. These temperature sensitive semiconductor detector substrates include some of the currently most promising inter-metallic materials, such as Cadmium Telluride (CdTe) compositions and Cadmium Zinc Telluride (CdZnTe) compositions.
When bonding high density semiconductor substrates together with solder, the interconnection volumes are very small in the resulting imaging devices. This small interconnect area coupled with the relatively more brittle character of some of the promising inter-metallic detector substrates can result in a decrease in the mechanical stability of the interconnection and decreased reliability when solder bump-bonding is used with some of these inter-metallic materials. Additionally, the use of metallic Lead (Pb) in solder to bond the semiconductor substrates increases the amount of this toxic metal potentially exposed to the environment.
Therefore, it would be beneficial to the industry to have a semiconductor substrate bonding technique that does not subject the brittle and temperature sensitive inter-metallic semiconductor materials to excessive heat or pressure. Additionally, it would be beneficial to the industry to have an alternative method for producing semiconductor imaging substrates that is simpler than the current bonding techniques, less susceptible to the problem of cold solder joints or cold welds, and which reduces the amount of metallic lead required to accomplish the bonding process.